For directly operating an articulated robot installed on a production line to teach the articulated robot working attitudes, the operator who is familiar with operating the articulated robot needs to work at the site of the production line. Therefore, the working time is limited and the operation is inefficient. Since it is necessary to perform the teaching process while the production line is being shut off, the operating rate of the production line is reduced.
In recent years, teaching off line (off-line teaching) has been practiced in order to perform the teaching process efficiently or increase the operating rate of the production line. Specifically, a model of an articulated robot, a workpiece to be worked and surrounding structures is constructed on a computer, and teaching data is generated using the model. Thereafter, the teaching data is supplied to the articulated robot on site. In this manner, it is possible to generate teaching data efficiently without shutting off the production line.
Production lines have been required to increase their productivity. To meet the requirement, attempts are made to shorten the cycle time of articulated robots. Under the circumstances, there has been proposed a technology for calculating attitudes of an articulated robot at respective working points in a working sequence, selecting attitudes of the articulated robot for short moving times and reduced end effector attitude differences, thereafter calculating an attitude of the articulated robot at a final working point in a reverse working sequence, and comparing the calculated attitude of the articulated robot at the final working point with the attitude of the articulated robot at a final working point in the working sequence, and correcting the calculated attitude of the articulated robot (see, for example, Japanese Laid-Open Patent Publication No. 2003-94363). The proposed technology is preferable because it can shorten the cycle time of operation of the articulated robot for increased productivity.
There has also been proposed a method of automatically setting the insertion path and attitude of an end effector with respect to a workpiece for generating teaching data for the articulated robot (see, for example, Japanese Laid-Open Patent Publication No. 2002-239955 and Japanese Laid-Open Patent Publication No. 2002-239957).
According to the process disclosed in Japanese Laid-Open Patent Publication No. 2003-94363, since teaching data is established mainly for the purpose of reducing the end effector attitude differences, the moving path between working points for the end effector may not be smooth. When the end effector works successively on the successive working points, the time to apply the end effector to the first working point and the time to remove the end effector from the final working point are not sufficiently taken into account. As a result, the overall cycle time may be increased, and the operator may need to correct the teaching data on a trial-and-error basis.
Teaching data is generated by establishing working points and a working sequence of an articulated robot with respect to a workpiece, determining robot attitudes at the respective working points, then establishing working details for the workpiece at the respective working points as working attributes, and establishing moving processes between the working points as moving attributes. Data of the robot attitudes at the working points occasionally includes tool coordinate data representative of the attitudes of an end effector mounted on the tip end of the robot.
Off-line teaching does not require the production line to be shut off. If off-line teaching is performed inefficiently, however, it is necessary to use the teaching computer for a long period of time, and a large burden is posed on the operator who performs the teaching process. An articulated robot to be trained is positioned in the vicinity of a given conveyor line for welding vehicles that are conveyed on the conveyor line. However, the vehicles conveyed on the conveyor line may not be limited to one type. When the type of vehicles to be processed by the articulated robot is to be changed, new teaching data needs to be generated.
There has been proposed a technology applicable where there is existing teaching data. According to the proposed technology, if the existing teaching data includes data that can be used on a preferential basis to provide an attitude for a new working point, the data is utilized (see, for example, Japanese Laid-Open Patent Publication No. 2003-117864). The proposed technology is preferable because new teaching data can be generated using existing teaching data.
According to the technology disclosed in Japanese Laid-Open Patent Publication No. 2003-117864, however, the portion of the existing teaching data that can be utilized as new teaching data is limited, and the existing teaching data may not be utilized if workpieces change their shape. Under the circumstances, it has been desirous to further effectively utilize existing teaching data.    Patent document 1: Japanese Laid-Open Patent Publication No. 2003-94363    Patent document 2: Japanese Laid-Open Patent Publication No. 2002-239955    Patent document 3: Japanese Laid-Open Patent Publication No. 2002-239957    Patent document 4: Japanese Laid-Open Patent Publication No. 2003-117864